There are almost as many oil wells in some geographical locations as there are people. Some of these wells are free flowing with an envious production rate and usually quite valuable because they make a lot more money than it costs to operate the well. There are other oil wells that show a marginal profit due to the low production rate and the costly upkeep, and often at the end of the month a loss is sustained rather than the desired profit, because it has cost more to operate the well than the money received from selling the produced oil. For example, Fort Stockton, Tex., is located in the Chihuahuaian desert, and has numerous hydrocarbon producing wells such as described above. Many of these marginal wells are owned by individuals who personally operate and maintain the wells, as contrasted to the more profitable wells which usually are owned by the large oil companies. An individual owner-operator can often operate a well at a profit whereas the same well, if operated by a large company, will probably show a loss. Large companies usually will not operate a well at a loss unless ulterior motives are involved.
These marginal wells often require a pumpjack unit to lift the crude to the surface of the earth, which increases the cost of operation. The produced fluid is sometime very corrosive and this causes everything contacted by the fluid to rapidly deteriorate. This deterioration causes holes to appear in the tubing, the rod string to deteriorate and break, as well as malfunction of the downhole pump, and many other problems that can be associated with scale and other debris that results from the downhole corrosion that is going on all the time unless something is done to counteract this expensive, deleterious, and undesirable destruction.
Whenever these downhole problems interrupt the production it is necessary to call out an expensive pulling unit or workover rig and pull whatever is defective from the borehole. Sometime this includes thousands of feet of the rod string and the tubing string in order to retrieve the downhole pump or to replace the tubing string.
It would therefore be desirable to be able to chemically inhibit the entire borehole and flow lines connected thereto in a manner which would reduce the rate of corrosion to an acceptable value by the employment of appropriate treatment chemicals. It would also be desirable to be able to treat the well with various different treatment chemicals in a manner to assure that all of the metal parts of the equipment associated with the wellbore are properly coated, and thereby reduce the rate of corrosion to an acceptable value; as well as modifying the properties of the produced fluid and additionally preventing various other undesirable phenomena from occurring downhole in the borehole so that a marginal producer can be changed into a profitable operation.
Those skilled in the art of selling treatment chemicals for use downhole in a borehole have come up with dozens of different organic and inorganic chemicals that need to be considered for treatment of a borehole. Therefore, it is often desirable to treat a borehole with a plurality of different chemicals in order to achieve all of the above desirable protective expedients. However, when a plurality of chemicals are mixed together and stored for a long period of time, in some instances many of the beneficial characteristics of the chemical mixture is lost due to complex interaction that occurs amongst the different treatment compounds. On the other hand, even when these chemicals are maintained separate from one another until they are individually injected into the upper borehole annulus, they commence free falling down through the annulus and soon contact and cling to the interior surface of the casing wall and the exterior surface of the tubing wall where they can subsequently react with the sour gas, one another, and any other available reactant that may be present since they are exposed and coat a tremendous surface area. Moreover, it is only natural that an undesirably long time interval is involved before the treatment chemical reaches the downhole pump and formation. Most anything can happen to the chemical during this long interval of time.
The treatment of a marginal producer must therefore be judiciously planned and carefully carried out or there will still remain a lack of profit because it will now be shared between the pulling unit company and the chemical company, rather than accumulating to the benefit of the owner.
It would therefore be desirable to be able to treat a hydrocarbon producing well in a manner whereby low cost chemical treatment can be carried out in a dependable and economical manner, and with an efficiency which causes the well to produce for many months without any maintenance required on the well, and wherein the cost of treating the well becomes economically tolerable, whereby the sales of the crude produced by the well leaves a profit at the end of the month after the maintenance and chemical bills have been paid.
A method and apparatus for downhole chemical treatment of a wellbore which achieves the above desirable goal is the subject of the present invention.